Reduce memory peaks when generating data urls for images.

Adding Vector<char> to a String results in one (or more) temporary
copies of that Vector<char> since Vector isn't a pointer/smart pointer
like the types usually used.

Luckily there are many other ways to solve the problem. With StringBuilder
or using a String.

BUG=389085 (related to, not necessarily fixing it)

Review URL: https://codereview.chromium.org/559103002

git-svn-id: svn://svn.chromium.org/blink/trunk@181925 bbb929c8-8fbe-4397-9dbb-9b2b20218538

third_party/WebKit/Source/core/inspector/InspectorLayerTreeAgent.cpp

@@ -53,6 +53,7 @@
 #include "public/platform/WebFloatPoint.h"
 #include "public/platform/WebLayer.h"
 #include "wtf/text/Base64.h"
+#include "wtf/text/StringBuilder.h"
 
 namespace blink {
 
@@ -383,7 +384,11 @@ void InspectorLayerTreeAgent::replaySnapshot(ErrorString* errorString, const Str
         *errorString = "Image encoding failed";
         return;
     }
-    *dataURL = "data:image/png;base64," + *base64Data;
+    StringBuilder url;
+    url.appendLiteral("data:image/png;base64,");
+    url.reserveCapacity(url.length() + base64Data->size());
+    url.append(base64Data->begin(), base64Data->size());
+    *dataURL = url.toString();
 }
 
 void InspectorLayerTreeAgent::profileSnapshot(ErrorString* errorString, const String& snapshotId, const int* minRepeatCount, const double* minDuration, RefPtr<TypeBuilder::Array<TypeBuilder::Array<double> > >& outTimings)

third_party/WebKit/Source/platform/graphics/ImageBuffer.cpp

@@ -415,10 +415,8 @@ String ImageBuffer::toDataURL(const String& mimeType, const double* quality) con
     Vector<char> encodedImage;
     if (!isSurfaceValid() || !encodeImage(m_surface->bitmap(), mimeType, quality, &encodedImage))
         return "data:,";
-    Vector<char> base64Data;
-    base64Encode(encodedImage, base64Data);
 
-    return "data:" + mimeType + ";base64," + base64Data;
+    return "data:" + mimeType + ";base64," + base64Encode(encodedImage);
 }
 
 String ImageDataToDataURL(const ImageDataBuffer& imageData, const String& mimeType, const double* quality)
@@ -429,10 +427,7 @@ String ImageDataToDataURL(const ImageDataBuffer& imageData, const String& mimeTy
     if (!encodeImage(imageData, mimeType, quality, &encodedImage))
         return "data:,";
 
-    Vector<char> base64Data;
-    base64Encode(encodedImage, base64Data);
-
-    return "data:" + mimeType + ";base64," + base64Data;
+    return "data:" + mimeType + ";base64," + base64Encode(encodedImage);
 }
 
 } // namespace blink